The invention involves a marked plate for a rotational angle sensor element for rotating structural parts, in particular, rotating shafts, with many angle marks provided preferably oriented radially to the rotational axis and preferably arranged in the form of a collar arranged concentrically to the rotational axis and with at least one reference mark, furthermore, an angular sensor element for use with the marked plate, and including a fixed sensor unit for the angle marks, including at least one transmitter of electromagnetic radiation and at least one receiver for the radiation modulated by the marked plate, as well as mechanisms for connection to an evaluation unit, and also a process for determining a reference value from an analog signal, which is obtained by the modulation of a transmitter signal through many angle marks and at least one reference mark that deviates in the quality of the modulation relative to the angle marks, whereby the modulated signal is received by a receiver and supplied to an evaluation unit and digitalized further if need be.
The measurement and display of the current angular position of a rotating part in real time, i.e., with negligibly small signal delay, is necessary in many areas of technology. For example, both in research and development, as well as in the mass-production application of internal combustion engines, angular sensor elements for the current angular position of the crankshaft or the camshaft(s) are used. For this, different measurement principles are used.
An especially advantageous system uses an angle marked plate, which can be mechanically connected to the rotating part, and a sensor device for scanning the angle marks that are located on the plate and typically arranged radially to the rotational axis and preferably concentrically around this axis. For this purpose, two measurement channels are provided with which two lines of angle marks are scanned independently of each other using two sensor systems, namely an incremental track with many equal angle marks that are equidistant, for example, 720 angle marks per revolution, and a reference track with, for example, one reference mark per revolution. The rotational angle position of the plate—and thus also the rotating part—can be determined from the angle mark signals of the incremental track and in reference to the reference marks—which, for example, can identify the position of the upper dead center of one of the cylinders of a piston engine. The sensory device is preferably an electro-optical system, which scans the angle marks by transmitted light or by reflected light and after a possible digitalization, supplies them to a display and/or evaluation device. In the process, the form of the angle marks and the sensitivity characteristic of the sensors are tuned to each other, preferably also the radiation emission characteristic of the transmitter, whereby in general, lengthwise, slit-type transmission and receiving windows are oriented to dash-shaped angle marks, both radially to the rotational axis and essentially parallel to each other. For the conditioning of the sensor signals, an analog electronic system is provided with the smallest possible time delay, whereby from the amplified analog signals of the angle mark sensors, using fast comparators, digital trigger signals are derived that show the time point at which the respectively associated rotational angle has been reached. Digital signal processors until now have not proven themselves worthy because of the calculation times and the unavoidable time delay associated with them, whereas the system explained above especially ensures, in a manner that is clear to the user, the absolute angle position measurement of a rotating part with high precision and angle resolution and with a negligibly small time delay between a specific position of the part and the output of the associated electric signal.
However, systems like those explained above have the disadvantage that the two—or in cases of several tracks, even several opto-electrical measurement channels are expensive, require space and do not contribute in an insignificant manner to the weight and/or the mass of the measurement arrangement. Both structural size as well as mass are decidedly disruptive, especially for small engines with high rotational speeds, in which each additional (centrifugal) mass on the crankshaft can be clearly noticed, or for engines already installed in vehicles and the spatial ratios that are narrowed as a result and/or also in relation to the large centrifugal accelerations, to which the measurement device is exposed in practical operation in internal combustion engines.
As a result, simple and inexpensive solutions have been proposed, which have only one measurement channel, often an inductive sensor, and for which the reference position is given by a deviation from the otherwise equidistant arrangement of the angle marks. For example, in collar gears, teeth are left out in order to identify the reference position. Using the currently measured rotational angle speed and/or from the expected time duration of the following rotational angle interval, the evaluation unit detects the missing teeth and shows that the reference position has been reached. By extrapolation from the respectively preceding duration of a rotational angle interval, the missing angle mark signals can also be simulated. However, this is associated with the significant disadvantage of the clearly reduced accuracy of the continuous rotational angle measurement since in the angle mark gaps necessary for the coding of the reference position, the current rotational angle information is missing, so that both the reference position as well as the current rotational angle speed can only be given approximately. Moreover, the necessary calculations require a significant time delay. Thus, a system of this type for research and development, for analysis of rotational unevenness and rotational vibrations of internal combustion engines, for example, or also the precise crankshaft-synchronous measurement data detection, is too imprecise or only conditionally useable.